1. Field of the Invention
The present invention relates to a sheet perforation device for forming holes in a sheet by punching at predetermined positions on the sheet.
2. Description of the Related Art
Sheet sorters are known that sort sheets of paper ejected from image forming apparatuses such as copying machines and bind the sheets by means of stapling.
In recent years, sheet sorters have also been proposed of a type having a punching unit which punches holes in successive sheets ejected from an image forming apparatus so as to form holes at predetermined positions in each of the successive sheets. The punching unit is disposed along the path of travel of the ejected sheets so that the sheets are perforated as they move through the punching unit. The pitch, or spacing, of the holes formed by the perforation device is fixed.
The use of this type of punching unit, however, has the following problems. If the punching unit is designed to form two holes, and if the sheet to be perforated has a dimension equal to or less than the spacing between the holes, the sheet is not perforated because the sheet is between the punchers, or the sheet may be imperfectly perforated such that one or both edges of the sheet are notched in a crescent form. Such imperfectly perorated sheets must be discarded. Ejection of a sheet having no perforation at all when the punching function is activated may lead the user to the erroneous conclusion that the punching failure is attributable to a malfunction of the apparatus.